Variable permeability device



April 1969 J. J. MUNNELLY 3,436,705

VARIABLE PERMEABILITY DEVICE Filed Nov. 24, 1967 Sheet of 2 FIG. 3B

MAGNET/ZAT/ON CHARACTER/ST/C CURVES 0.3 I AMPERES lNVENTO/P J. J MUNNE LL Y BY Mm ATTORNEY Z of 2 Sheet Filed Nov. 24, 1967 United States Patent US. Cl. 336-132 '8 Claims ABSTRACT OF THE DISCLOSURE Stepless changes in the bilateral impedance of an inductor are effected independently of flux density by building laminated cores of material exhibiting a directionally dependent permeability. Selected ones of the core laminations are alignable with respect to the others which are fixed.

This invention relates to variable impedance devices and more specifically to devices which make use of a variable permeability characteristic.

Background of the invention In power supply circuitry and elsewhere it often is desirable to obtain a stepless manual change in impedance. Common devices which achieve this today include reactors with turns adjusted by means of winding taps or sliding contacts, inductors with means to alter the core area or magnetic path reluctance, and inductors which utilize the Curie effect.

The present invention concerns a new and, for many applications, preferred alternative to these devices, with which stepless changes in the bilateral impedance of an inductor can be effected at any useful value of flux density. In basic principle, the device modifies circuit reluctance by providing alternate parallel flux paths which redistribute the flux within a core configuration. In broadest terms, the variable permeability feature of the present invention traces to the relative alignment of areas of different permeabilities within the device.

In one practical embodiment, an inductor core built as a sequence of rings from material exhibiting a directional permeability dependence may be adjusted in impedance by the rotation of, for example, alternate rings. Importantly, this may be achieved at any useful value of flux density. Grain-oriented silicon steel is one material exhibiting the desired property of directional permeabilty dependence.

One object of the invention is to provide a new and simplified variable reluctance device.

A more specific object of the invention is to achieve truly stepless changes in the impedance of an inductor at any useful value of flux density.

A feature of the invention resides, therefore, in the utilization of the relative alignment of areas of different permeability for varying the reluctance and hence the impedance of a device.

A further feature of the invention is that in the inventive device the flux path within the core itself is changed, thus making for a device with fewer parts.

The invention, its further objects, features and advantages will be readily comprehended in reading the descriptions to follow of several illustrative embodiments thereof.

Description of the drawing FIGS. 1 and 2 are perspective drawings of a variable permeability device constructed pursuant to the inventive teachings;

FIG. 3A is a schematic diagram of one core ring;

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FIG. 3B is a graph demonstrating E-I characteristics of the device of FIG. 1;

FIG. 4 is a schematic diagram of an alternative ring;

FIG. 5 is a further type of ring structure in schematic view;

FIG. 6 is a still further variation shown in schematic perspective; and

FIG. 7 is a still further form of the invention shown in schematic perspective.

FIG. 1 illustrates a first embodiment of the invention. Shown there and in FIG. 2 is an inductor which comprises a core designated generally as 10 made up of ring laminations. In the example shown, the odd rings designated 11 are fixed as by a bar 12 engaging through inward flanges 13 of the rings 11. Even numbered rings designated 14 are movable, that is, rotatable around a common axis 15, through manipulation of outer flanges 16. As shown in FIG. 1, a conventional winding 17 is emplaced around the core, with connections (not shown) available between the winding 17 and an external circuit.

Although this first embodiment used rings with inner and outer flanges, it can be readily seen that a plurality of a single basic part, a ring lamination such as ring 14 for example, exhibiting a directionally dependent permeability, is all that is required in the core construction.

The ring laminations 11, 14 are stampings from sheets of grain-oriented silicon steel or like material which exhibits a directionally dependent permeability factor. Specfically, the permeability of grain-oriented silicon steel varies depending on the angle of the flux path to the grain orientation. FIGS. 3A and 3B illustrate the practical consequences of this fact applied to the instant device in accordance with principles of the invention.

Thus, as seen in FIG. 3A a typical ring lamination (either 11 or 14) when made with grain-oriented silicon steel exhibits two areas in which permeability is highest. These areas are designated 19 and are 180 degrees removed from one another. Intermediate the areas 19, about degrees removed, are the areas corresponding to the lowest permeability and designated 20. In practice, areas 20 are not quite as localized as the high permeability areas. In the ring lamination shown in FIG. 3A, the grain orientation is always in the same direction as indicated by the arrow 21.

FIG. 3B represents the magnetization curves, designated A and B, obtained by manipulating the movable rings. Curve A corresponds to the alignment of areas of high and of low permeability. Curve B corresponds to the alignment of areas of about equal permeability. With a flux density maintained constant as, for example, at 10 kilogauss, a change in impedance (as represented by AI) between the extremes of adjustment as high as fifty percent can take place.

This change in impedance can be explained in the following way. When unequal permeability areas are adjacent to each other in adjacent rings, substantial flux shunting takes place from the low to the high permeability areas. The overall reluctance of the magnetic path is thereby reduced and the impedance is increased. When the areas of equal permeability are adjacent to each other in adjacent rings negligible flux transfer occurs between adjoining laminations since the core is magnetically homo geneous at any given cross section.

An important aspect of the invention is that since an infinite number of curves lying between curves A and B may be obtained at intermediate movable ring positions, a continuous and stepless change in core permeability is realized. Thus, advantageously, a controlled alteration of permeability in a closed magnetic circuit is achieved without using additional material, D-C bias, air gaps or external electrical magnetic energy; and furthermore achieved without a change in geometry of the coil employing the magnetic circuit.

An interesting feature of the embodiment of the invention illustrated in FIGS. 1 and 2 is that a rotation of 90 degrees is required for a maximum change in permeability at a low flux density; but at high flux density near saturation a rotation of only 50 degrees of the movable rings is required for the maximum permeability change.

In grain-oriented silicon steel, the permeability as a function of the angle between the flux path and grain orientation is quite marked and is dependent on the flux density. For example, at kg. the permeability is onehalf of the maximum for that density for a 30 degree flux-grain angle change, while at kg. for a degree flux-grain angle change the permeability is one-twentieth of the maximum possible at that density. The required change in flux-grain angle for maximum and minimum permeability conditions can be improved, i.e., achieving the same change but with less rotation, by introducing into the basic ring more than two areas of highest permeability.

As seen in FIG. 4, this may be accomplished by punching segments of a ring from grain-oriented silicon steel, rather than punching a complete ring; and assembling them as seen in that figure. Specifically, six segments 22 each comprising a sector of 60 degrees can be punched out so that each segment contains a central area where the flux-grain angle is as near zero as practical. These segments then are butt-welded together to form a single planar continuous lamination, which after a stress-relief anneal has six areas within the ring of high permeability separated by six areas of low permeability. Accordingly if the structure shown in FIG. 1 is constructed with rings depicted in FIG. 4, then the required angle of mechanical rotation of the movable rings with respect to the stationary rings to obtain a maximum and minimum permeability condition is about 30 degrees for flux densities below the knee of the magnetization curve and in the order of 17 degrees for flux densities approaching saturation. This represents an improvement over the original configuration in two respects. First, more area is available for the winding; and secondly, less rotation is required.

A further adaptation of the concept of high permeability segments just described involves arranging the welding process so that rather than closed rings, a continuous spiral of the segments is formed. The resulting structure is shown in schematic FIG. 5. Two such spiral laminations 22a, 22b are then threaded together or interleaved to form a toroidal core. One end of the stationary spiral lamination 22a is fastened to the inside of a core box or enclosure. One end of the movable spiral lamination 22b is affixed to a rotating means such as lever 220 which moves lamination 22b in the direction of arrow 22d. A winding 22e passes around and through the core.

A structure employing the inventive principles which permits unlimited rotation of the movable rings in either the clockwise or counterclockwise directions is shown in FIG. 6. Two types of rings are required for this structure. One type 25 of thickness T has outer tabs 26 and is completely flat. The other type 27 of thickness T has as an integral part an internal strip 28 of thickness 2T, its center being on an inside diameter of the ring, with its upper surface 29 flush and common to the upper surface of the ring. The opposite surface of strip 28 extends an amount T beyond the lower surface of the ring. The protruding portion of ring 27 conforms to the inside diameter of the ring 25, in order to minimize the air gap in the flux path between strip 28 and ring 25, and which also serves as a bearing to guide the rotation of the rings 27. Using the core configuration of FIG. 6, a winding 31 is placed around strips 28; and means are provided for rotating the center winding section relative to rings 25. The rings 25, 27, may contain two or more localized areas of high permeability as shown in FIG. 3A or 4. It thus is readily seen that an unlimited amount of rotation is possible between the first and second rings, a potentially desirable feature in some device applications.

A further variation of the inventive concept is depicted in FIG. 7 and involves two or more concentric cylinders closely fitted. An inner cylinder 35 rotates within fixed outer cylinder 36 anchored to base plate 36a, with a winding 37 covering 270 or thereabouts but rotating with cylinder 35. As with previously described devices, the movable member may be attached to a lever 38 and an indicating scale 39. The cylinders 35, 36 may be formed of stacks of grain-oriented silicon steel rings of suitable dimensions. It is common practice to form such a cylinder of ring laminations by aligning the rings, compressing the stack, and then apply a liquid cement (ambroid, epoxy, etc.) to the inside or outside circumference in order to bond the rings together. The rings may have two or more localized areas of high permeability as outlined previously, with like areas of permeability covering like areas of permeability in adjacent rings with this alignment maintained in individual cylinders. A given radial cross section of such a cylinder would be magnetically homogeneous. The outside diameter of the inner cylinder rings is slightly less than the inside diameter of the outer cylinder rings in order to minimize the air gap between surfaces, yet permit free rotation. Either cylinder (if only two are used) may be made the movable part.

In all of the described configurations where some part of the cores move relative to the winding, it is implicit that the cores must be at least partially surrounded by a rigidly insulating closure or core box. This enclosure protects the insulation on the wire from abrasion by the movable core and isolates the core laminations from the compressive force of the wire of the winding. In the illustrations the core box is omitted for simplification.

It is to be understood that the embodiments described herein are merely illustrative of the principles of the invention. Various modifications may be made thereto by persons skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

1. A variable impedance device comprising: a core comprising a first and a second set of rings, each ring being fabricated from material exhibiting a directionally dependent permeability; means for rotating said second ring set with respect to said first ring set; and winding means disposed around and through said ring sets.

2. A device in accordance with claim 1 wherein each ring comprises two diametrically opposed areas of relatively high permeability and two diametrically opposed areas of relatively low permeability separated by about degrees from the first-mentioned areas.

3. A device in accordance with claim 1 wherein each ring comprises a plurality of joined segments, each segment comprising an area of relatively high permeability in the center thereof and an area of relatively low permeability in the junction zone between segments.

4. A variable impedance device comprising: a core comprising first and second continuous spirals interleaved with one another, each spiral comprising a plurality of joined segments and each segment having an area of relatively high permeability in the center thereof with the junction between segments exhibiting relatively loW permeability; means for maintaining said first spiral stationary and for moving said second spiral rotationally with respect to the first; and winding means disposed around said first and second spirals.

5. A variable impedance device comprising: a core comprising first and second ring sets alternately interleaved, the rings in said first set being flat and including outer tabs, and each ring in said second set having an internal strip centered on an inside diameter of the adjacent second ring set, said strip having a protruding bearing portion that conforms to said inside diameter, all rings being fabricated from material exhibiting a directionally dependent permeability; winding means placed around said strips; and means for rotating said strips thereby to move said second ring set with respect to said first ring set.

6. A device in accordance with claim 5, wherein the thickness of each said strip is twice the thickness of the rings of said first and said second set, said rings being of equal thickness.

7. A variable impedance device comprising a fixed outer cylinder and a concentric inner cylinder, each cylinder being formed of stacks of rings formed from a material exhibiting a directionally dependent permeability, the areas of high permeability of each ring being in substantial alignment in each cylinder so formed; Winding means disposed around and through said outer and inner References Cited UNITED STATES PATENTS 7/1944 Polydoroif 336-132 XR 6/1965 Peek et al. 336 218 XR LEWIS H. MYERS, Primary Examiner. T. J. KOZMA, Assistant Examiner.

US. Cl. X.R. 

